The term oxymethylene polymer as used herein is meant to include oxymethylene homopolymers and diethers and diesters. Also included are oxymethylene copolymers, which include oxymethylene polymers having at least 50 percent recurring oxymethylene units and at least one other unit derived from a monomer copolymerizable with the source of the oxymethylene units.
Oxymethylene polymers having recurring --CH.sub.2 O-- units have been known for many years. They may be prepared for example, by the polymerization of anhydrous formaldehyde or by the polymerization of trioxane, which is a cyclic trimer of formaldehyde, and will vary in physical properties such as thermal stability, molecular weight, molding characteristics, color and the like depending, in part, upon their method of preparation, on the catalytic polymerization technique employed and upon the various types of comonomers which may be incorporated into the polymer.
The polyacetal resins are superior in mechanical and physical properties and, therefore, have been widely used in various fields, especially as molding resins. It is known that polyoxymethylenes can be provided with additives in order to improve certain physical properties of the molding resin, and as well the molded products obtained therefrom. Such additives extend the range of possible uses of such polymer compositions. Thus, fillers have been incorporated into the oxymethylene polymers for the purpose of improving rigid strength, hardness, friction resistance and wear resistance, to increase heat distortion temperature, impart fire retardancy, increase dimensional accuracy of the molded articles by decreasing shrinkage, improve electrical conductivity and antistatic property, and to increase economy by using inexpensive fillers. U.S. Pat. No. 4,506,053 cites numerous inorganic and organic fillers which can be included in the form of powder, flakes, or fibers in oxymethylene polymer compositions. Among the vast list of materials disclosed in the patent are included metal silicates such as talc, clay, mica, asbestos, calcium silicate, montmorillonite and bentonite which materials are similar to the low gloss additives used in the present invention to be further discussed.
It is important to recognize that while the use of a particular filler may impart a desired property to the oxymethylene polymer composition, the addition of the filler may also degrade certain other properties. Thus, it is important that the particular filler used achieve improvements in the desired physical property and not degrade the good mechanical properties of polyacetal resins if its use is to be accepted by industry.
One proposed use for polyacetal resins is as molded components in the interior of automobiles. One necessary property of any molded product in an automobile interior is that the surface of the molded article have a low-gloss in order to aesthetically match interior coverings such as seat upholsteries and the like. As before said, it is important that the use of a filler to reduce the gloss of a polyacetal resin not significantly alter the other properties. Thus, the primary objective of the present invention is to provide a low-gloss polyacetal polymer composition which retains its mechanical properties.